Some transmissive image display apparatuses such as liquid crystal display apparatuses use a direct surface light source device. In recent years, surface light source devices having a plurality of light emitting elements as the light sources have been used.
For example, the surface light source device includes a substrate, a plurality of light emitting elements, a plurality of light flux controlling members, and a diffusion plate. The plurality of light emitting elements is disposed on the substrate in a matrix. The light flux controlling member for expanding light emitted from each of the light emitting elements in the plane direction of the substrate is disposed over each of the light emitting elements. The light emitted from each of the light emitting elements is diffused by the light flux controlling member to irradiate a member to be irradiated (e.g., liquid crystal panel) in a planar manner (see, e.g., PTL 1).
FIG. 1 illustrates a configuration of a back light device (surface light source device) disclosed in PTL 1. As illustrated in FIG. 1, back light device 10 disclosed in PTL 1 includes mounting substrate 20, package 30 disposed on mounting substrate 20 and emitting light through its upper surface, diffusion lens (light flux controlling member) 40 disposed on mounting substrate 20 in such a manner as to cover package 30 to control the distribution of light emitted from package 30, and diffusion plate 50 that transmits light emitted from diffusion lens 40 while diffusing the light. Diffusion lens 40 has lens part 41 for expanding light emitted from package 30, and fixing part 42 for fixing lens part 41 to mounting substrate 20 via adhesive 46. Lens part 41 has bottom surface 43 closer to mounting substrate 20, recessed light incidence surface 44 opening toward bottom surface 43, and light emission surface 45 disposed opposite to light incidence surface 44.
The light emitted from package 30 enters diffusion lens 40 through light incidence surface 44. The light having entered diffusion lens 40 is emitted toward the outside of diffusion lens 40 through light emission surface 45. Then, the light emitted toward the outside is transmitted through diffusion plate 50 while being diffused to thereby irradiate a member to be irradiated in a planar manner.
In addition, PTL 2 discloses a flip-chip type LED that emits light from the side surface. The LED disclosed in PTL 2 is designed to emit light from the side surface by disposing a reflective film on the upper surface of a phosphor layer that emanates light.